Etching device

ABSTRACT

An etching device for supplying an etchant to the surface of a workpiece held on a rotating spinner table, which comprises a center portion supply nozzle for supplying the etchant to the rotation center portion of the workpiece held on the spinner table and a peripheral portion supply nozzle for supplying the etchant to an area between the rotation center portion and the periphery of the workpiece.

FIELD OF THE INVENTION

[0001] The present invention relates to an etching device for etching a workpiece such as a semiconductor wafer held on a rotating spinner table by applying an etchant to the surface of the workpiece.

DESCRIPTION OF THE PRIOR ART

[0002] In the production of a semiconductor device, a circuit is formed in a large number of areas arranged in a form of a lattice on the surface of a semiconductor wafer and each area having the circuit formed therein is diced to produce a semiconductor chip. To improve the heat radiation property of the semiconductor chip, the thickness of the semiconductor chip is desirably made as small as possible. Further, to enable the downsizing of portable telephones, smart cards, personal computers and the like in which a large number of semiconductor chips are used, the semiconductor chip is desirably formed as thin as possible. To this end, before the semiconductor wafer is divided into chips, the back surface of the semiconductor wafer is ground to a predetermined thickness. However, when the thickness of the semiconductor chip is made small by grinding the back surface of the semiconductor wafer, the breaking strength of the semiconductor chip is reduced by the influence of fine cracks or distortion formed by grinding, thereby reducing the yield and shortening the service life of a product. To cope with these problems, in the step of processing the semiconductor wafer, the back surface of the semiconductor wafer is subjected to an etching treatment to remove the fine cracks or distortion generated by grinding after the grinding of the back surface of the semiconductor wafer in order to improve the bending strength and further reduce the thickness of the semiconductor chip.

[0003] As the etching device for etching the semiconductor wafer is generally used a so-called spin etching device which comprises a spinner table for holding and turning a semiconductor wafer as a workpiece and an etchant supply nozzle for supplying an etchant to the rotation center portion of the workpiece held on the spinner table, and supplies an etchant containing, for example, nitric acid and hydrofluoric acid from the etchant supply nozzle.

[0004] When the ground surface of the semiconductor wafer as a workpiece is etched by the spin etching device, there arises such a problem that the amount of etching increases in an area of from the center portion toward the periphery of the semiconductor wafer, that is, the semiconductor wafer is thick at its center portion and becomes thinner toward its periphery. For example, when a semiconductor wafer having a diameter of 200 mm is etched by the spin etching device and its center portion is etched 20 μm, its peripheral portion is etched 30 μm or more. As the amount of etching increases, the difference in thickness between the center portion and the peripheral portion of the semiconductor wafer becomes larger. When a semiconductor wafer having a diameter of 300 mm is etched by the spin etching device and its center portion is etched 20 μm, its peripheral portion is etched 50 μm or more. As the diameter of the semiconductor wafer as a workpiece becomes larger, the amount of the peripheral portion etched increases cumulatively. This is a problem that cannot be ignored.

SUMMARY OF THE INVENTION

[0005] It is an object of the present invention to provide an etching device capable of reducing the difference between the amount of etching at the center portion and that at the peripheral portion of a workpiece.

[0006] The inventor of the present invention has conducted intensive studies and has found that the temperature of an etchant supplied to the rotation center portion of a workpiece having a diameter of approximately 300 mm is raised by friction heat and an activation caused by rotation and accumulated reaction heat. That is, for example, even the temperature at the center portion is approximately 20° C., the temperature at the peripheral portion is raised up to approximately 70° C. It is considered that the reaction rate is accelerated due to this rise in the temperature of the etchant, so that the amount removed of etching increases with the approach to the periphery of the workpiece. Accordingly, the inventor of the present invention has found that the difference between the amount of etching at the center portion and that at the peripheral portion of the workpiece can be reduced by cooling the etchant at the periphery of the workpiece.

[0007] To attain the above object, according to the present invention, there is provided an etching device comprising a spinner table for holding a workpiece and turning it and an etchant supply means for supplying an etchant to the surface of the workpiece held on the spinner table, wherein

[0008] the etchant supply means comprises a center portion supply nozzle for supplying the etchant to the rotation center portion of the workpiece held on the spinner table and a peripheral portion supply nozzle for supplying the etchant to an area between the rotation center portion and the peripheral portion of the workpiece.

[0009] The above peripheral portion supply nozzle desirably has a plurality of nozzles provided at positions different in distance from the above center portion supply nozzle. The amount of the etchant supplied from the above peripheral portion supply nozzle is desirably set larger than the amount of the etchant supplied from the above center portion supply nozzle.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a schematic diagram showing an embodiment of an etching device constituted according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] A preferred embodiment of the etching device of the present invention will be described in further detail with reference to the accompanying drawing.

[0012]FIG. 1 shows an etching device constituted according to the present invention. The etching device comprises a spinner table 2 for holding a workpiece to be etched, such as a semiconductor wafer. This spinner table 2 is rotatably mounted and has a flat circular base 21 which is substantially horizontal at the top. An electric motor 3 is connected to the spinner table 2 as a drive source via an appropriate power transmission mechanism (not shown). When the electric motor 3 is driven, the spinner table 2 is turned at a predetermined revolution speed.

[0013] A carrying means 4 schematically shown in FIG. 1 is disposed relative to the spinner table 2. In the illustrated embodiment, the workpiece to be etched is a substantially disk-like semiconductor wafer 5 made from silicon, and the carrying means 4 may be a known means which can vacuum-adsorb the semiconductor wafer 5 at the end of a movable arm to carry it through a predetermined route. This carrying means 4 carries, for example, one semiconductor wafer 5 discharged from a grinding machine to the top of the spinner table 2 and then, carries out the etched, rinsed and dried semiconductor wafer 5 from the top of the spinner table 5 to a predetermined position (etching, rinsing and drying of the semiconductor wafer 5 will be referred to later). The semiconductor wafer 5 is carried to the top of the spinner table 2 in such a state that it is inverted, that is, its back surface faces up. A circuit (not shown) is formed in a large number of sections arranged in a lattice form on the top surface of the semiconductor wafer 5, that is, the undersurface of the semiconductor wafer 5 in a state where it is placed on the spinner table 2. A protective film (not shown) which can be formed of an appropriate synthetic resin film is affixed to the top surface of the semiconductor wafer 5. The back surface of the semiconductor wafer 5, that is, the upwardly exposed top-side surface of the semiconductor wafer 5 in a state where it is placed on the spinner table 2 is ground by a grinding machine (not shown) also called “back grinder” before it is carried to the top of the spinner table 2 and therefore has a distortion caused by grinding. Etching is carried out for the purpose of removing the distortion. The outer diameter of the semiconductor wafer 5 placed on the spinner table 2 is slightly larger than the outer diameter of the circular base 21 of the spinner table 2.

[0014] In the illustrated embodiment, the spinner table 2 is provided with an air-spray means 6. This air-spray means 6 has a passage 61 which extends from below the spinner table 2 to the periphery of the spinner table 2 and then along the undersurface of the semiconductor wafer 5 placed on the spinner table 2. Air supplied from a compressed air source (not sown) flows along the undersurface of the semiconductor wafer 5 from the periphery of the spinner table 2 to prevent the etchant applied to the top-side surface of the semiconductor wafer 5 from flowing onto the undersurface of the semiconductor wafer 5. The spinner table 2 is further provided with an etchant collection means 7 for collecting the etchant applied to the top-side surface of the semiconductor wafer 5 on the spinner table 2. This etchant collection means 7 consists of a static member 71 and a movable member 72 which form a collection tank in cooperation with each other. The static member 71 has a cylindrical outer wall 711, an annular bottom 712 and a cylindrical inner wall 713. The movable member 72 has a cylindrical lower portion and an upper portion having an arcuate cross section. While the etchant is applied to the top-side surface of the semiconductor wafer 5 on the spinner table 2, the movable member 72 is located to an upper position indicated by solid lines in the FIG. 1 so that the etchant flowing radially over the top-side surface of the semiconductor wafer 5 is caused to flow into the etchant collection means 7 from an annular inlet 73 formed between the upper end of the inner wall 713 of the static member and the upper end of the movable member 72. To rinse the semiconductor wafer 5 with a cleaning fluid which may be pure water, the movable member 72 is moved to a lower position indicated by two-dot chain lines in the FIG. 1 so that the annular inlet 73 is closed to prevent the cleaning fluid from flowing into the etchant collection means 7.

[0015] The illustrated etching device comprises an etchant supply means 8 for supplying the etchant to the semiconductor wafer 5 held on the spinner table 2. The etchant supply means 8 in the illustrated embodiment comprises an etchant storage tank 81. This etchant storage tank 81 contains the etchant 82 to be applied to the top-side surface of the semiconductor wafer 5 which is made from silicon and placed on the top of the above spinner table 2. This etchant 82 is an aqueous solution containing nitric acid and hydrofluoric acid. The etchant 82 in the etchant storage tank 81 is supplied to the top-side surface of the semiconductor wafer 5 on the spinner table 2 via a feed pipe 84 by a pump 83. The etchant supply means 8 in the illustrated embodiment comprises a center portion supply nozzle 85 for supplying the etchant to the rotation center portion of the semiconductor wafer 5 held on the spinner table 2 and two peripheral portion supply nozzles 86 a and 86 b for supplying the etchant to an area between the rotation center portion and the periphery of the semiconductor wafer 5. These nozzles are connected to the above feed pipe 84. The two peripheral portion supply nozzles 86 a and 86 b are arranged at positions different in distance from the center portion supply nozzle 85. The left peripheral portion supply nozzle 86 b in the FIG. 1 is disposed at a position farther from the center portion supply nozzle 85 than the right peripheral portion supply nozzle 86 a. The center portion supply nozzle 85 and the two peripheral portion supply nozzles 86 a and 86 b are constructed to be selectively moved to a working position (position shown in FIG. 1) above the semiconductor wafer 5 placed on the spinner table 2 and a non-working position where they are retreated from above the semiconductor wafer 5.

[0016] The depicted etching device in the illustrated embodiment comprises an etchant discharge means 9 for discharging the etchant collected in the collection tank of the above etchant collection means 7. This etchant discharge means 9 consists of a drain pipe 91 connected to a discharge port (not shown) formed in the annular bottom 712 forming the collection tank of the etchant collection means 7 and a drain tank 92 for storing the etchant discharged through the drain pipe 91.

[0017] The depicted etching device in the illustrated embodiment is constituted as described above and its function will be described hereinafter.

[0018] Etching is carried out by activating the pump 83 of the etchant supply means 8 to spray the etchant 82 in the etchant storage tank 81 toward the top-side surface of the semiconductor wafer 5 from the center portion supply nozzle 85 and the peripheral portion supply nozzles 86 a and 86 b through the feed pipe 84. As known to people of ordinary skill in the art, when the etchant 82 containing nitric acid and hydrofluoric acid is sprayed onto the top-side surface of the semiconductor wafer 5 made from silicon, an oxidation reaction represented by the following formula takes place as a first stage:

Si+2HNO₃→SIO₂+NO₂+NO+H₂O

[0019] followed by a dissolution reaction represented by the following formula as a second stage:

SiO₂+6HF→H₂SiF₆+2H₂O.

[0020] Therefore, the etching of the semiconductor wafer 5 made from silicon can be represented by the following formula:

Si+2HNO₃+6HF→H₂SiF₆+3H₂O+NO₂+NO.

[0021] Under the condition that a sufficient amount of nitric acid is existing, the etching rate is determined by a concentration of hydrofluoric acid and the temperature of the etchant 82. Accordingly, to set a predetermined etching rate, it is important that the temperature of the etchant 82 should be set to a predetermined value, the content of nitric acid in the etchant 82 is set to excessive and the content of hydrofluoric acid should be set to a predetermined value.

[0022] To etch the semiconductor wafer 5 by supplying the etchant 82 to the top-side surface of the semiconductor wafer 5 on the spinner table 2, the spinner table 2 is turned at approximately 600 rpm, whereby the etchant 82 sprayed from the center portion supply nozzle 85 and the peripheral portion supply nozzles 86 a and 86 b is caused to flow over the entire top-side surface of the semiconductor wafer 5 fully uniformly. The air-spray means 6 fitted onto the spinner table 2 causes air to flow along the undersurface of the semiconductor wafer 5 from the periphery of the spinner table 2, thereby preventing the etchant 82 from being contacted to the undersurface, that is, the top surface of the semiconductor wafer 5. The movable member 72 of the etchant collection means 7 is positioned to the upper position indicated by the solid lines in the FIG. 1 and the etchant 82 caused to flow over the top-side surface of the semiconductor wafer 5 is collected in the etchant collection means 7. The etchant 82 collected in the etchant collection means 7 is discharged into the drain tank 92 through the drain pipe 91 of the etchant discharge means 9.

[0023] In the above etching step, the temperature of the etchant supplied from the center portion supply nozzle 85 to the center portion of the semiconductor wafer 5 as the workpiece placed on the spinner table 2 is raised by accumulated reaction heat and by friction heat and an activation caused by rotation as it moves toward the periphery of the semiconductor wafer 5. However, since the peripheral portion supply nozzles 86 a and 86 b for supplying the etchant are provided in the area between the rotation center portion and the periphery of the semiconductor wafer 5 held on the spinner table 2 in the illustrated embodiment, the etchant which is supplied to the center portion of the semiconductor wafer 5 from the center portion supply nozzle 85 and whose temperature rises as it moves toward the periphery is cooled by the etchant supplied from the peripheral portion supply nozzle 86 a. Although the temperature of the etchant supplied from the above center portion supply nozzle 85 and the peripheral portion supply nozzle 86 a rises as it moves toward the periphery, the etchant is cooled by the etchant supplied from the peripheral portion supply nozzle 86 b provided farther from the center portion supply nozzle 85 than the peripheral portion supply nozzle 86 a. Since the etchant supplied from the peripheral portion supply nozzles 86 a and 86 b thus functions as a cooling fluid in the illustrated embodiment, the temperature of the etchant supplied to the semiconductor wafer 5 which is the workpiece does not rise as it moves toward the periphery. Therefore, the temperature of the etchant on the semiconductor wafer 5 is equalized, thereby making it possible to equalize the reaction rate, reduce variations in the amount of etching, and control variations in the thickness of the etched semiconductor wafer 5 within an allowable range. It is desirable that the etchant supplied from the peripheral portion supply nozzles 86a and 86b should be supplied toward the center portion side and not directly toward the periphery to act on the etchant moving from the center portion side toward the periphery. To enhance the cooling effect of the etchant supplied from the peripheral portion supply nozzles 86 a and 86 b, it is desirable that the amount of the etchant supplied from the peripheral portion supply nozzle 86 a should be made larger than that of the etchant supplied from the center portion supply nozzle 85 and should be made smaller than that of the etchant supplied from the peripheral portion supply nozzle 86 b.

[0024] As described above, after completion of the etching step for etching the semiconductor wafer 5 placed on the spinner table 2 by applying the etchant 82 to the top-side surface of the semiconductor wafer 5, the semiconductor wafer 5 on the spinner table 2 may be rinsed as required and dried. In the rinsing step, the center portion supply nozzle 85 and the peripheral portion supply nozzles 86 a and 86 b for supplying the etchant 82 are retreated from the working position above the semiconductor wafer 5 to the non-working position and a jet nozzle (not shown) for spraying a cleaning fluid which may be pure water is positioned above the semiconductor wafer 5 to spray the cleaning fluid onto the top-side surface of the semiconductor wafer 5. At this point, the movable member 72 of the etchant collection means 7 is moved down to the lower position indicated by the two-dot chain lines in the FIG. 1 to close the annular inlet 73 of the etchant collection means 7 so as to prevent the cleaning fluid from entering the etchant collection means 7. The semiconductor wafer 5 can be dried by so-called spin drying that allows to rotate the spinner table 2 at a high speed, for example, approximately at 2,000 to 3,000 rpm.

[0025] While the present invention has been described based on the illustrated embodiment, the present invention is not limited to the embodiment. In the illustrated embodiment, the present invention is applied to the etching device of the type in which the etchant collected in the etchant collection means 7 is discharged into the drain tank 92 of the etchant discharge means 9. The present invention can also be applied to an etching device of a recycling type in which the etchant collected in the etchant collection means 7 is recycled to the etchant storage tank 81. Since the etchant is supplied from the center portion supply nozzle and the peripheral portion supply nozzles in the present invention, the amount of the etchant supplied is larger than that of the prior art. Therefore, application of the etching device of the present invention to the etchant recycling type etching device is effective.

[0026] Since the etching device of the present invention comprises a center portion supply nozzle for supplying an etchant to the rotation center portion of a workpiece held on the spinner table and peripheral portion supply nozzles for supplying the etchant to an area between the rotation center portion and the periphery of the workpiece, the etchant supplied from the center portion supply nozzle to the center portion of the workpiece and having temperature elevated as it moves toward the periphery is cooled by the etchant supplied from the peripheral portion supply nozzles. Therefore, the temperature of the etchant supplied to the workpiece does not rise as it moves toward the periphery and the temperature of the etchant on the workpiece is equalized, whereby the reaction rate is equalized, variations in the amount of etching are minimized, and variations in the thickness of the etched workpiece are small and can be controlled within an allowable range. 

What is claimed is:
 1. An etching device comprising a spinner table for holding a workpiece and turning it and an etchant supply means for supplying an etchant to the surface of the workpiece held on the spinner table, wherein the etchant supply means has a center portion supply nozzle for supplying the etchant to the rotation center portion of the workpiece held on the spinner table and a peripheral portion supply nozzle for supplying the etchant to an area between the rotation center portion and the periphery of the workpiece.
 2. The etching device of claim 1, wherein the peripheral portion supply nozzle has a plurality of nozzles provided at positions different in distance from the center portion supply nozzle.
 3. The etching device of claim 1, wherein the amount of the etchant supplied from the peripheral portion supply nozzle is set larger than the amount of the etchant supplied from the center portion supply nozzle. 